Chemotaxis is the movement of an organism in response to chemicals in its environment. There are two types: positive chemotaxis where an organism moves toward an attractant, and negative chemotaxis where it moves away from a repellent. Bacteria like E. coli use runs and tumbles to navigate chemical gradients - detecting increases in attractants which reduces tumbling, and increases in repellents which increases tumbling. Chemotaxis allows bacteria in soil to move toward nutrient-rich root exudates from plants, potentially forming symbiotic relationships. Factors like chemical compounds, temperature, pH, and water potential can influence bacterial chemotaxis.

1. CHEMOTAXIS
Presented By-
HARIOM
M.sc. Zoology Semester-II
Department Of Zoology
BBAU LUCKNOW

2. INTRODUCTION
• Chemotaxis - Composed of two words “chemo + taxis”.
• Chemo means a “chemical substance” is a form of matter that has constant chemical composition
and characteristic properties.
• Taxis means "arrangement" is the movement of an organism in response to a stimulus such as light
or the presence of food.
• Chemotaxis is the movement of an organism/bacteria in response to a chemical stimulus i.e.,
move away or towards substances that are present in the environment through a non-random
process.
This movement is two type of chemotaxis-
 Positive chemotaxis
 Negative chemotaxis

3. TYPES OF CHEMOTAXIS
 Positive chemotaxis- The movement of organism towards a chemical is called
positive chemotaxis. e.g. food nutrients
 Negative chemotaxis- The movement of organism away from the chemical is
called negative chemotaxis . e. g. toxins
 Chemoattractants - Chemicals that attract bacteria. e.g.,for E.coli amino acids (serine and
aspartic acid), sugars (maltose, ribose, galactose, glucose), dipeptides, pyrimidines and electron
acceptors (oxygen, nitrate, fumarate).
• Chemorepellents - Chemicals that drive bacteria away. e.g., for E.coli amino acid (leucine),
metal ion (Ni), pH, potentially noxious chemicals (alcohols and fatty acids).

4. History of Chemotaxis
 The migration of microbes is observed after the development of microscopy.
 The first description is given by T.W.Engelmann(1881),W.F.Pfeffer(1884) in bacteria and
H.S.Jennings in ciliates
 Nobel laureate E.Metchnikoff also contributed in this research
 At this time definitions for this phenomenon are also made
 In 1970,1960’s revolution in microbiology created many techniques used to study this
phenomenon .
 On November 2006,Dr.Dennis Bray of Cambridge university got Microsoft European science
award for his work on chemotaxis taking place in E.coli.

5. Chemotaxis Behavior
 E. coli moves up a gradient of
attractant -
 Detects a net positive change in
attractant concentration,
 Reduces the probability of a tumble
and tends to continue going up the
gradient.
 Swim/Runs - the cell keeps a rather
constant direction which produce
Counter clockwise rotation.
 The runs last about 1 sec on average.

6. Chemotaxis Behavior Continued…..
 E. coli detects a concentration of
repellent increases with time -
 The cell increases tumbling
frequency,
 Tends to change direction and
avoid swimming toward repellents.
 Tumbles - the bacterium stops and
randomly changes direction which
produce Clockwise rotation
 The tumbles about 0.1 sec on
average.

7. CHEMOTAXIS IN SOIL
 Many bacteria is growing near to the roots of some plants this is because of
the exudates of roots in the rhizosphere region.
 So during plant growth the bacteria in the soil moved towards the roots
exudates using the chemotactic activity to get nutrient.
 The root exudates contain vitamins , sugars,
Organic acids , amino acids,etc which attracts the bacteria in the soil.

8. CONT’D
 In rice fields, the chemotaxis cause movement of beneficial microbes towards
the roots which are involving in nutrient cycle, protection to the plants etc.
 They may create symbiotic relationship with the Plants.
 They may attract pathogens to the plant.
 For example isoflavin secreted by the root of Soya bean attracts a mutualist
(Bradyrhizhobium japonicum)and also a pathogen(Phytopthora sojae).

9. FACTORS AFFECTING CHEMOTAXIS
 Chemical compounds present in the place affects the movement of microbes.
For example, if the chemical is nutritive or useful to the bacteria it cause
positive chemotaxis.
 If it is toxic or not useful to that then it cause negative chemotaxis.
 Temperature also affects this. For example p.florescence have good
chemotactic activity at 30ºc .
 Other than these, chemotactic activity is affected by pH,water potential etc.
 The water potential affects bacterial flow and the secretion of root exudates.

10. USE OF CHEMOTAXIS IN RHIZOBIUM
 The plants of leguminaceae release a particular enzyme to attract the
microbes .
 The rhizobium bacteria is attracted using chemotaxis and they produce signal
of their arrival to the plant and cause the formation of root nodules.

11. REFERENCES
 www.biomentors.online
 slideshare
 www.researchgate.net
 Chemotaxis Methods and Protocols
Tian Jin
Dale Herald